SUMMARY/ABSTRACT The quality of primary care in the United States is suboptimal. Researchers, policymakers, and practitioners have proposed a number of interventions over the years to address perceived and realized problems within primary care practices. The development of patient centered medical homes (PCMH) is a recent and promising approach to improving primary care. Although the evidence to date on the effectiveness of the PCMH model has been mixed, some studies have suggested that successful transformation of practices into PMCHs will lead to improvements in quality, reductions in costs, and improvements in both patient-centeredness and provider satisfaction. However, successful PCMH transformation will likely require substantial financial investment. When the financial investment is insufficient, practices may not achieve successful transformation and, therefore, not meet the goals of the PCMH model. Little is known about the financial investment necessary to ensure successful transformation. Because these financial estimates do not exist, payers, policymakers, and practice leaders can never be sure that their investments are sufficient to achieve successful transformation. In order to address this important issue, we will employ mixed method, multiple case study design based on semi-structured interviews with practice representatives, financial records, and cost surveys in order to quantify the one-time/ongoing and direct/indirect costs of PCMH transformation. Our estimates will be a first and important step to informing payers and policymakers regarding the optimal level of investment.